Method for pretreatment of filler, modified filler with a hydrophobic polymer and use of the hydrophobic polymer

ABSTRACT

A modified filler used in the making of paper or the like, preparation of the filler and its use. The modified filler comprises a filler known as such, e.g. calcium carbonate, kaolin, talc, titanium dioxide, sodium silicate and aluminiumtrihydrate or their mixture, and a hydrophobic polymer made of polymerisable monomers, which is added to the filler as a polymer dispersion or a polymer solution.

[0001] The present invention relates to a method defined by thepreambles of the independent claims presented below for pretreatment ofa filler used in the making of paper, board or the like, to a modifiedfiller and to its use.

[0002] Fillers used in the making of paper and board are for instancecalcium carbonate, such as precipitated calcium carbonate (PCC), kaolin,such as calcinated kaolin, talc, titanium dioxide, sodium silicate andaluminiumtrihydrate. Also mixtures of the above mentioned minerals canbe used as fillers.

[0003] An object of paper makers, particularly makers of fine paper, isever more to increase the filler content of paper due to cost reasons.However, due to a highly increased filler content the paper loses instrength, stiffness and other mechanical characteristics. A high fillercontent also increases the linting of paper. As a high filler contentfor instance an amount can be considered, which calculated as dry mattercomprises >20% of the amount of the fibre suspension. An addition of abinding agent can affect the above-mentioned characteristics. Anaddition of binding agent can i.a. increase the strength of the finishedpaper.

[0004] Among other materials starch has been conventionally used as abinding agent. Starch is a hydrophilic material, which added in largeamounts assists water to penetrate into the paper web. Thus the use ofstarch has also negative effects, particularly on the wet strength ofthe paper.

[0005] The use of starch can also have disadvantageous effects in thepost-treatment of the paper, and for instance during printing it cancause too strong an absorption of the printing ink into the paper. Alsoother liquids, such as surface sizing agents and coatings may beabsorbed in a non-desired manner into the paper.

[0006] Other hydrophilic binding agents, such as hydrophilic syntheticpolymers, may cause the same problems as starch.

[0007] The object of the present invention is to provide an improvedmethod for pretreatment of filler used in the making of paper, board orthe like, a modified filler and its use.

[0008] Then the object is to provide such a method and an additive forthe pretreatment of a filler which enables also large additions of thefiller without the great disadvantages caused by the absorption of watermentioned above.

[0009] In order to attain the above-mentioned objects the method and thefiller according to the invention are characterised in what is definedin the characterising parts of the independent claims presented below.

[0010] A typical method according to the invention for pretreatment offiller used in the making of paper, board or the like comprises theaddition of a hydrophobic polymer made of polymerisable monomers to thefiller in order to create a hydrophobic film on the surface of thefiller particles and/or between adjacent filler particles. The filler ispretreated with the hydrophobic polymer so that it makes it moredifficult for water to penetrate into the filler layer. Thus, thepretreatment of the filler can improve the wet strength and reduce thelinting of the paper, board or the like to be made.

[0011] The addition of a hydrophobic polymer to the filler means in thisdescription the combination of the polymer and the filler with eachother. The combination can be made by mixing the polymer to the filleror by mixing the filler to the polymer. The combination can also be madeso, that both materials are supplied simultaneously to the fibresuspension at the same dispensing point, so that the mixing occurs inthe dispensing conduit immediately before reaching the fibre suspension.The mixing occurs at a high shear force.

[0012] The advantages of the invention are manifested particularly whena hydrophobic polymer is added to the filler in papermaking using highamounts of filler, over 20%, typically more than 25% of the dry solidscontent of the paper. In the solution according to the invention thehydrophobic polymer added to the filler is mainly a polymer which doesnot have to react covalently with the filler or with the cellulose fibrein order to create a barrier which restricts the penetration of water orincreases retention. In the solution according to the invention thehydrophobic polymer forms a film-like barrier around the fillerparticles and between them. Previously reactive sizes where the effectrestricting the penetration of water is created only when the sizesreact with the fibres have been used in the papermaking. These sizes arenot film creating polymers, whereby they do not create a film on thefiller surface, and thus they do not reduce paper linting. Further, whenthey react with the fibre they prevent the creating of bonds between thefibres, and thus they have a negative effect on the paper strengthproperties.

[0013] The polymer added to the filler is typically a polymer which iscreated by solution or emulsion polymerisation with polymerisablemonomers, and which has a molecular weight >5000, typically >10,000. Inspecial cases the polymer can also contain a minor portion of smallerpolymer molecules.

[0014] The polymer is added to the filler as a polymer dispersion or apolymer solution, which is polymerised using as a stabilising agentpolysaccharide, such as starch, mannan and/or CMC. In addition it ispossible to use as the stabilising agent a synthetic polymer, such aspolyaminoamide or another polyaminopolymer, and/or a suitable dispersingagent, and/or anionic and/or cationic polymerisable monomers.

[0015] According to a preferred embodiment of the invention the polymercan be added to the filler as a polymer dispersion which is formed bycopolymerising a monomer mixture of a polysaccharide dissolved in water,the monomer mixture containing at least one vinylic monomer. Thetemperature at which the polymer made by copolymerisation generates afilm is about −50 to 200° C. typically 0 to 100° C. most typically 0 to70° C. Regarding the prevention of Tinting a temperature of 10 to 50° C.is preferred. In this case a dense film is formed on the surface of thefiller particles. However, the selected temperature depends on thetemperature conditions in the paper machine.

[0016] The polysaccharide used to prepare the polymer, for instancestarch, is chemically modified by cationic and/or anionic groups,whereby the substitution level (DS) regarding the cationic and/oranionic substituents is typically 0.1 to 2, most typically 0.1 to 1.

[0017] According to another preferred embodiment of the invention thepolymer can be added to the filler as a stable product which is formedby mixing starch in granule form into a synthetic polymer, such asstyrene maleic anhydrate (SMA), styrene maleic imide (SMI) or the like,and by letting the starch react with the polymer under the influence ofheat.

[0018] According to an advantageous embodiment of the invention thepolymer can be added to the filler as a polymer dispersion whichcomprises the following components, whose amounts are presented as drysolids content,

[0019] a) 5 to 50%, advantageously 5 to 40% starch having a substitutionlevel (DS) regarding cationic and/or anionic substituents of about 0.01to 1, typically 0.04 to 1.0, and an intrinsic viscosity of >1.0 dl/g inthe cationised and/or anionised state, typically 1.5 to 15 dl/g;

[0020] b) 50 to 95%, advantageously 60 to 95% of a monomer mixturecontaining at least one vinylic monomer, and

[0021] c) water.

[0022] The most typically used monomers in the preparation are forinstance styrene, 1,3-butadiene, butylacrylate, metyl methacrylate,ethyl acrylate, 2-ethyl hexyl acrylate, acrylonitrile, acrylamide,methacrylamide and vinyl acetate. Also cationic and/or anionic monomerscan be used in the preparation, such as acrylic acid, methacrylic acidand chloride of trimethyl ammonium propylmethacrylamide.

[0023] The temperature at which the polymer which is formed by a monomermixture will generate a film is typically 10 to 50° C. advantageously 20to 50° C.

[0024] The monomer mixture used in the preparation of the polymerdispersion can comprise e.g. about 40 to 70% acrylates and about 30 to60% styrene, whereby the monomer mixture can comprise of, for instance,the following components:

[0025] a) acrylonitrile, 0 to 19%, typically 5 to 19%, most typicallyabout 19%;

[0026] b) acrylates, 10 to 60%, typically 20 to 50%, most typicallyabout 30%, and

[0027] c) styrene, 10 to 60%, typically 20 to 40%, most typically about30%.

[0028] As an answer to the problems regarding wet strength and lintingin papermaking the solution according to the invention thus proposes theuse of an additive containing a hydrophobic polymer for pretreatment ofthe filler. In this case the additive is typically a hydrophobic polymermade of polymerisable monomers, which is added to the filler as apolymer dispersion or as a polymer solution in order to create ahydrophobic film on the surface of the filler particles and thus toimprove the characteristics of the paper or the like to be manufactured,such as to increase wet strength and to reduce linting. The polymer ismade of a monomer mixture containing at least one vinylic monomer.According to a preferred embodiment of the invention the polymer is madeof a monomer mixture containing at least acrylates and styrene. Themonomer mixture comprises e.g.

[0029] A) acrylonitrile or methacrylonitrile or a mixture of them;

[0030] b) acrylates; and

[0031] c) styrene or other copolymerable monomers unsubstituted byethylene.

[0032] The invention is illustrated with the aid of the enclosedexamples of embodiments.

EXAMPLE 1

[0033] Paper (80 g/m²) was prepared in a sheet mould where the fibreswere oriented with the aid of flow. In the preparation a cellulosemixture of birch and pine was used in proportion 70/30 beaten to about35° SR. The temperature of the fibre suspension was 45° C. In additionprecipitated calcium carbonate (PCC) was used as filler, at a level of25% of the total pulp composition. To the fibre suspension 1% pulpstarch with a cationic degree DS of 0.035 was also added. As retentionagents, which were dispensed after the filler addition, 0.05% Percol 162and 0.15% Hydrocol O were used. The results are shown in Table 1 below.TABLE 1 Geometric tensile strength Geometric ten- Active index of silestrength in- Test material Amount wet paper dex of dry paper Cobb₆₀ HSTpoint (%) (%) (Nm/g) (Nm/g) (g/m²) (s) 1 AKD 0.13 2.715 37.9 32.2 262 20.25 1.914 38.8 20.1 419 3 0.25 1.890 38.5 19.7 439 4 Starch 0.25 1.78542.3 19.7 407 5 0.50 1.701 48.8 21.5 376 6 SMA 0.25 2.079 45.8 18.5 5677 0.50 2.268 49.1 17.3 635 8 SA 0.25 2.117 38.5 19.9 479 9 0.50 2.34439.2 19.0 536

[0034] In test points 1 and 2 alkylketene dimer dispersion (AKD) wasmixed to the filler material before adding it to the fibre suspension.

[0035] In test point 3 the AKD was added to the fibre suspension, andthe filler without AKD addition was added.

[0036] In test points 4 to 9 the AKD was added to the fibre suspensionin a similar manner as in point 3, using the standard amount 0.25%, andthe other chemicals were admixed to the filler material before adding tothe fibre suspension. The chemical dosage was calculated to correspondto a certain percentage of active chemical of the paper's dry solidscontent.

[0037] In test points 4 and 5 starch was used, which had been used tostabilise the AKD dispersion, in order to illustrate the effect ofstarch in the test points 1 to 3.

[0038] In test points 6 and 7 ammonium salt of styrene maleic acid wasadded to the filler material, whereby the salt had been treated at anactive material ratio 1:1 with the same starch which was used in thetest points 4 and 5.

[0039] In test points 8 and 9 styrene acrylate acrylonitrile copolymer,the preparation of which is disclosed in more detail in the patentapplication PCT/FI100/00084, example 4.

[0040] The strength of the wet paper was determined from humid paper(dry solids content 45%) before drying.

[0041] In the example 1 it can be seen that AKD improves thehydrophobicity of the paper, but impairs the paper's strengthcharacteristics. The strength of the dry paper is obtained with thestarch used in dispersing the AKD. However, the starch reduces the wetstrength of the paper. Both SMA and styrene acrylate substantiallyimprove the strength properties of wet paper and have an improvingeffect also on the dry strength and on the hydrophobicity of the paper.

EXAMPLE 2

[0042] Paper (80 g/m²) was made in a test paper machine having a webwidth of 70 cm and the speed 80 m/min. In the making a cellulose mixtureof birch and pine in proportions 70/30 beaten to about 28° SR was used.In addition precipitated calcium carbonate (PCC) was used as filler, ata level of 25% of the total pulp composition. To the fibre suspension0.9% pulp starch with a cationic degree DS of 0.045 and 0.2% of AKDdispersion was also added, the dosage determined according to the AKDconcentration. As retention agents, which were dispensed after thefiller addition, we used 0.03% Percol 162 and 0.15% Hydrocol O.

[0043] In this example the styrene acrylate acrylonitrile copolymermentioned in example 1 was used as a variable, which was eitherdispensed to the fibre suspension before the filler, or mixed to thefiller. The dispensed amount was in both test points the same, 0.6% ofthe paper's dry solids content. The tensile strength of wet paper wasdetermined from paper which had been immersed in water so long that apaper's dry solids content of 45% was obtained. The results arepresented in Table 2 below. TABLE 2 Geometric ten- Geometric ten- silestrength in- sile strength Amount dex of wet paper index of dry Cobb₆₀HST of lint (Nm/g) paper (Nm/g) (g/m²) (s) (mg) Addition 1.051 32.2422.0 114 41.7 to the fibre suspension Addition 1.154 32.56 20.2 184 35.8to the fill- er

[0044] In the table it can clearly be seen that the addition of thehydrophobic polymer provides a better wet strength value and lintingvalue, when the addition is made to the filler instead of to the fibresuspension. In the table it can be seen that the paper linting is muchlower when the hydrophobic polymer is dispersed to the fibre suspensionafter it has been admixed to the filler, compared to a situation wherethe polymer would have been dispersed directly to the fibre suspension.The dispersion to the filler also had an impact on the paper's strengthand hydrophobicity.

[0045] The method according to this invention, where the filler ispretreated or modified by a hydrophobic material which creates a film,increases the hydrophobicity of the paper or the like, and at the sametime it improves the strength characteristics of both dry and wet paper.Further as advantages of the solution according to the invention can bementioned, that the method is able to reduce the paper linting.

[0046] The invention is not intended to be limited to the exemplaryembodiments presented above, but the intention is to be able toimplement the invention widely within the scope defined by the enclosedclaims.

1. A method for pretreatment of filler, such as calcium carbonate,kaolin, talc, titanium dioxide, sodium silicate and aluminiumtrihydrateor their mixture, used in the making of paper, board or the like, thepretreatment being conducted before the filler is supplied to the fibresuspension, characterised in that the pretreatment comprises theaddition of a hydrophobic polymer made of polymerisable monomers to thefiller in order to create a hydrophobic film on the surface of thefiller particles and/or between adjacent filler particles, and that thepolymer added to the filler is added as a polymer dispersion or apolymer solution, which polymer is polymerised using polysaccharide,such as starch, mannan and/or CMC as a stabilising agent, in order toimprove the characteristics of the paper, board or the like to be made,such as to increase the wet strength and/or reduce the linting.
 2. Amethod according to claim 1, characterised in that the polymer added tothe filler is a polymer, which is made by solution polymerisation oremulsion polymerisation of polymerisable monomers.
 3. A method accordingto claim 1, characterised in that the polymer added to the filler ismainly an inert polymer, which does not react covalently with the filleror with the cellulose fibre.
 4. A method according to claim 1,characterised in that the polymer added to the filler has a molecularweight, which is mainly over 5,000, typically over 10,000.
 5. A methodaccording to claim 1, characterised in that the polymer added to thefiller is added as a polymer dispersion or a polymer solution, which ispolymerised using further as a stabilising agent, a synthetic polymer,such as polyaminoamide or other polyaminopolymer, and/or some othersuitable dispersing agent, and/or anionic and/or cationic polymerisablemonomers.
 6. A method according to claim 1, characterised in that thepolymer is added to the filler as a stable product which is formed bymixing starch in granule form into a synthetic polymer, such as styrenemaleic anhydrate (SMA), styrene maleic imide (SMI) or the like, and byletting the starch react with the polymer under the influence of heat.7. A method according to claim 1, characterised in that the polymer tobe added to the filler is added as a polymer dispersion which is formedby copolymerising a monomer mixture of a polysaccharide dissolved inwater, the monomer mixture containing at least one vinylic monomer.
 8. Amethod according to claim 7, characterised in that the polysaccharide ischemically modified by cationic and/or anionic groups, whereby thesubstitution level (DS) regarding the cationic and/or anionicsubstituents is typically 0.1 to 2, most typically 0.1 to
 1. 9. A methodaccording to claim 7, characterised in that the temperature at which thepolymer made by copolymerisation creates a film is about −50 to 200° C.,typically 0 to 100° C., more typically 0 to 70° C., most typically 0 to50° C.
 10. A method according to claim 1, characterised in that thepolymer to be added to the filler is added as a polymer dispersion whichis comprised of the following components, whose amounts are presented asdry solids content, a) 5 to 50%, advantageously 5 to 40% starch having asubstitution level (DS) regarding cationic and/or anionic substituentsof about 0.01 to 1, typically 0.04 to 1.0, and an intrinsic viscosityof >1.0 dl/g in a cationised and/or anionised state, typically 1.5 to 15dl/g; b) 50 to 95%, advantageously 60 to 95% of a monomer mixturecontaining at least one vinylic monomer, and c) water.
 11. A methodaccording to claim 10, characterised in that the film generatingtemperature of the polymer which is formed by said monomer mixture istypically 10 to 50° C. advantageously 20 to 50° C.
 12. A methodaccording to claim 10, characterised in that the monomer mixturecomprises 40 to 70% acrylates and 30 to 60% styrene.
 13. A methodaccording to claim 10, characterised in that the monomer mixturecomprises a) acrylonitrile, 0 to 19%, typically 5 to 19%, most typicallyabout 19%; b) acrylates, 10 to 60%, typically 20 to 50%, most typicallyabout 30%, and c) styrene, 10 to 60%, typically 20 to 40%, mosttypically about 30%.
 14. A method according to claim 1, characterised inthat a hydrophobic polymer is added to the filler in the making ofpaper, which uses large amounts of filler, the amounts being >20%,typically >25%, of the dry solids content of the paper.
 15. A modifiedfiller to be used in the making of paper, board or the like, whichmodified filler comprises a filler known as such, e.g. calciumcarbonate, kaolin, talc, titanium dioxide, sodium silicate andaluminiumtrihydrate, characterised in that modified filler furthercomprises a hydrophobic polymer made of polymerisable monomers, whichpolymer is added to the filler as a polymer dispersion or a polymersolution, and which polymer is polymerised using polysaccharide, such asstarch, mannan and/or CMC as the stabilising agent, in order to create ahydrophobic film on the surface of the filler particles and/or betweenadjacent filler particles before the filler is supplied to the fibresuspension.
 16. A modified filler according to claim 15, characterisedin that the polymer is an inert polymer having a molecular weight, whichis over 5,000, preferably >10,000.
 17. A modified filler according toclaim 15, characterised in that the polymer is formed from a monomermixture containing at least one vinylic monomer.
 18. A modified filleraccording to claim 15, characterised in that the polymer is formed froma monomer mixture containing a) acrylonitrile or methacrylonitrile or amixture thereof, b) acrylates, c) styrene or other copolymerisablemonomers unsubstitued by ethylene.
 19. A modified filler according toclaim 15, characterised in that the polymer is formed from a monomermixture containing a) 0 to 19%, preferably 5 to 19%, most preferablyabout 19%, of acrylonitrile; b) 10 to 60%, preferably 20 to 50%, mostpreferably about 30% acrylates, and c) 10 to 60%, preferably 20 to 40%,most preferably about 30% styrene,
 20. A modified filler according toclaim 15, charactensed in that the polymer dispersion is comprised ofthe following components, whose amounts are presented as dry solidscontent, a) 5 to 50%, advantageously 5 to 40% starch having asubstitution level (DS) regarding cationic and/or anionic substituentsof about 0.01 to 1, typically 0.04 to 1.0, and an intrinsic viscosityof >1.0 dl/g in a cationised and/or anionised state, typically 1.5 to 15dl/g; b) 50 to 95%, advantageously 60 to 95% of a monomer mixturecontaining at least one vinylic monomer, and c) water.
 21. The use of ahydrophobic polymer made of polymerisable monomers for modifying afiller, such as calcium carbonate, kaolin, talc, titanium dioxide,sodium silicate and aluminiumtrihydrate or their mixture, used in themaking of paper, board or the like, characterised in that the polymer isadded to the filler as a polymer dispersion or a polymer solution, andwhich polymer is polymerised using polysaccharide, such as starch,mannan and/or CMC as a stabilising agent, before the filler is suppliedto the fibre suspension.
 22. The use according to claim 21,characterised in that the polymer is formed from a monomer mixturecontaining at least one vinylic monomer.
 23. The use according to claim21, characterised in that the polymer is added as a polymer dispersionformed from the following components, whose amounts are presented as drysolids content, a) 5 to 50%, advantageously 5 to 40% starch having asubstitution level (DS) regarding cationic and/or anionic substituentsof about 0.01.to 1, typically 0.04, to 1.0, and an intrinsic viscosityof >1.0 dl/g in a cationised and/or anionised state, typically 1.5 to 15dl/g; b) 50 to 95%, advantageously 60 to 95% of a monomer mixturecontaining at least one vinylic monomer, and c) water.
 24. The useaccording to claim 23, characterised in that the monomer mixturecomprises 40 to 70% acrylates and 30 to 60% styrene.